1. Field of the Disclosure
The present disclosure generally relates to: a threshold estimation apparatus which, in a short time, estimates a threshold of the intensity of stimulation applied to a living subject that is required for evoking a response of the living subject; a threshold estimation method; and a non-transitory computer-readable information recording medium storing a program.
2. Discussion of the Background Art
Conventionally, studies have been conducted on the functional analysis of a living subject by determining a threshold of the intensity of a stimulus applied to the living subject that is required for evoking a response of the living subject (see Patent Literature 1 and Non-Patent Literature 3). Further, there have also been proposed methods of applying the thus determined threshold to rehabilitation (see Non-Patent Literatures 1 and 2).
For example, there are tests being conducted where the presence or absence of a motor evoked potential (MEP) is detected by stimulating the somatosensory and motor cortices of the brain of a rat or the like through electrocorticogram electrodes and measuring the resulting electromyogram potential of the forelimb extensor digitorum muscle or hindlimb soleus muscle and the distribution of the electrodes, that is, thresholds of the stimulus intensity required for MEP to be generated in response to the stimulation at the respective positions of the motor cortex, is thereby determined. Such distribution of thresholds is referred to as “functional brain map”. Functional brain maps obtained by electrical stimulation are used in both clinical and basic studies.
Stimulation of a living subject is performed not only by electrical stimulation via an electrode such as an invasive electrode or a non-invasive electrode but also by magnetic stimulation via a coil or the like as well as other electromagnetic stimulation means. In the present disclosure, such an electrode, coil or the like utilized for application of electrical or magnetic stimulation is generally referred to as “stimulator”.
For instance, in clinical settings, functional brain mapping is carried out during brain surgery of a patient with seizure or brain tumor by arranging surface electrodes such as epidural electrocorticogram electrodes and applying stimuli via the surface electrodes. For example, a performer of ablative operation refers to a functional brain map and pays attention not to damage any region believed to have a critical function.
Meanwhile, in basic research, functional brain mapping is often carried out by intracortical microstimulation (ICMS) using needle electrodes. For example, electrical stimuli are applied to a restricted area of cortex via needle electrodes and a functional map of motor cortex is prepared based on the muscle action evoked by the stimuli and the stimulus intensity.
Generally speaking, for a deeper analysis of the functions of a living subject, it is necessary to prepare a functional map that represents, in the form of a threshold distribution, how the threshold of the stimulus intensity at which a response can be evoked in the living subject varies depending on the stimulated spots.
In conventional technologies, for example, at least 30 minutes is required to prepare a single functional brain map using 32 electrodes. Coupled with such a long time required for the preparation, it is conventionally believed that a functional brain map is static and does not change with time.